Tesla is currently trading at $256 a share, up 70% so far this year. While this trajectory has been interrupted by a couple of pretty steep pullbacks (shares fell as low as $116 in November), upward momentum was quickly restore on the broadly held conviction that visionary CEO Elon Musk’s electric-car and stored-energy (lithium-ion batteries) businesses are brilliantly conceived and executed, and will radically redefine transportation.

That’s great, but for folks like Achilles, the vision gets clouded by the numbers. Despite mediocre second quarter results (Tesla posted a net loss of $62 million), the company now has a $33 billion market cap, has a price/earnings ratio of 60, a price/sales ratio of 13, and is trading at 80 times forward earnings, all of which Achilles refers to as “indefensible valuations.”

Meanwhile, he points out Tesla’s free cash flow went even deeper into negative territory, hitting $177 million compared with $7 million a year ago, adding that even Elon Musk went on the record last year as saying Tesla shares might be overvalued, back when they were fetching $160.

“What we see with Tesla in the marketplace is a prime example of herding behavior and investors speculating on further short-term momentum. However, this seems to be an inherently unstable situation,” Achilles writes. “Tesla’s valuation has certainly run way ahead of its fundamentals even after considering second quarter 2014 results, which were (wrongfully) cheered by investors.”

But does that make Tesla the short of the decade? Some investors might agree. According to FactSet, 19.3% of Tesla’s shares are held in short positions. But the rest of the herd isn’t buying it. Wall Street analysts continue to bump up their price target on the company, which is now averaging $246.71, and 50% of them have a buy recommendation on the stock, up from 40% just a month ago and just 31% in April.

Nevertheless, some investors are clearly not adverse to locking in some recent gains. Tesla shares were last down 0.3% Wednesday at $256, just two days after hitting an all-time high of $267.26.

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